The illegal use of doping in competitive sport is strictly controlled worldwide by the World Anti-Doping Agency (WADA). It is important to note that not all athletes who test positive have doped knowingly and willingly. Prolactin is a hormone secreted by the pituitary gland. Besides its main role in regulating the milk flow in nursing mothers, prolactin influences various biological processes. In animal studies, the growth of the adrenal glands was directly correlated to prolactin, together with an additional increase in the production of androgens. Androgens are steroid hormones that cause a male appearance and promote the growth of muscles. The effect of prolactin on the secretion of androgens in the human adrenal gland is currently controversial. We therefore want to examine the effects of prolactin on the release of steroid hormones, especially androgens of the adrenal gland. For this purpose, we are examining patients who have a prolactinoma - a tumor of the pituitary gland. This tumor secretes high concentrations of prolactin, which gives us the opportunity to examine the effect of prolactin before and after treatment of the prolactinoma.